From the Editors of The Daily Cat
According to Michael W. Fox, author of The New Animal Doctor’s Answer Book, some cats “simply quit purring altogether for no apparent reason and others never purr.” Fox believes it’s just “an idiosyncrasy.”
In your case, your cat is purring since you can feel a vibration in his neck. If you put a microphone up to your cat’s neck, you’d likely hear the familiar sound. Remember: From an evolutionary standpoint, cats likely developed the ability to purr in order to communicate with their mothers when they were nursing as kittens. The vibration, which a mother cat can feel, tells her of the kitten’s presence and that all is OK.
A very ill cat will also sometimes purr. The real reason is still unknown: Some theories suggest the cat is attempting to calm itself, while others suggest the cat is trying to communicate submission to others. In any case, it’s perfectly normal for your adult cat to not emit a very audible purr. If it looks happy, butts you and comes to greet you, then it is expressing its contentment in other ways.